1. Field of the Invention
This invention relates to a sintered electrode for electrochemical processes, especially for the electrochemical winning of metals, which is corrosion-resistanct under electrolysis conditions, as well as a method for manufacturing the electrode.
2. Description of the Prior Art
Because of the strong corrosive attack under the conditions of the electrolysis, only few materials such as graphite, lead, nickel and platinum are suitable as electrodes, especially the anode, in processes for the electrochemical winning of metals. From the German Published Non-Prosecuted Applications 1 796 220 and 26 36 447, electrodes for this purpose are known which consist of a carrier or a base of titanium and a coating which covers the surface of the carrier and contains to a substantial extent manganese dioxide. Since the surface of the carrier of such electrodes is passivated under the electrolysis conditions in spite of the activation coating and the cell voltage rises in the process for constant current density, the electrodes can generally be operated only with rather low current densities. It is known to delay the passivation of the electrode carrier by a special coating consisting of several layers. According to German Published Non-Prosecuted Application 26 57 97 9, the covering layer applied to the carrier consisting of a metal that can be passivated, is composed of a coating layer consisting of an intermediate layer which contains oxides of tim and antimony, and of a cover layer which consists substantially of manganese dioxide. An anode is known from the French Provisional Patent No. 2 236 027, which on a sintered carrier of metallic titanium has a first manganese dioxide layer formed by thermal decomposition of a manganese compound, and a second manganese dioxide layer which is deposited electrochemically.
The preparation of coatings consisting of several individual layers is relatively expensive and, in addition, passivation of the carrier can be prevented only if the diffusion of oxygen ions through the layers is completely inhibited or is, at least, very small.